This invention relates to air duct outlet silencers, and in particular to silencers designed for use with gas turbines and other noise-creating, gas flow-producing devices.
Stationary gas turbines for the production of power are well known for use by power producing industries. One difficulty that is encountered with the use of gas turbines is the noise that they can create during their operation. Because of this noise, efforts have been made in the past to provide sound attenuators or sound reducing devices both at the intake of the gas turbine and at the outlet end. However for various reasons problems have been encountered in developing satisfactory inlet silencing units and outlet silencing devices for these gas turbines. One reason for these difficulties is that the flow into and out of stationary gas turbines is often compromised because of spacial constraints and cost factors. Many such systems feature a short plenum box with a vertical inflow into the compressor of the turbine and an axial outflow. In the usual case, inlet silencers are installed ahead of the plenum while the gas turbine outlet is often dumped into a plenum which feeds a vertical exhaust section consisting of some form of silencer and exhaust stack.
Outside of the field of gas turbines, both air duct inlet silencers and air duct outlet silencers have been developed in recent years for use in combination with axial fans providing air to large structures such as office buildings and industrial buildings. For example U.S. Pat. No. 5,587,563 issued Dec. 24, 1996 to Dipti K. R. Datta describes both an air inlet silencer for an axial fan and an air outlet silencer, both of which employ sound attenuating material located behind perforated sheet metal walls. The duct inlet silencer includes an exterior housing that has two principal air inlets located on opposite sides of the housing. The unit also has a single air outlet located at one end of the housing. The two inlets and the outlet are connected by airflow passageways defined by interior walls and these passageways bend 90 degrees from the inlets to the outlet. Sections of the interior walls are made from the aforementioned perforated sheet metal. In one preferred embodiment the passageway from each inlet is divided into four quadrants with upper and lower quadrants separated by a horizontal divider.
With respect to the fan outlet silencer described in the aforementioned U.S. patent, it has a top, bottom, and sidewalls and between these walls extend first and second series of splitters with the splitters of each series being spaced apart to form smaller air passageways. The splitters of each series are mounted side by side in a row and the splitters of one series are staggered with respect to the splitters of the other series in a direction transverse to the direction of airflow. The sound attenuating material that is used in both the inlet silencer and the outlet silencer for an axial fan as described in this U.S. patent is standard sound attenuating material such as fibreglass bats stuffed between the interior walls and the exterior walls and into the interior of the splitters.
Up to the present time, there has been no suggestion that inlet and outlet silencers of this general type could be used in combination with relatively large, stationary gas turbines. One difficulty with the known outlet silencers designed for use with ordinary axial fans is that they are not able to withstand the high temperatures that exist in the hot air stream emitted by the gas turbine nor are they able to withstand the much higher air velocities which can be as much as 15000 feet/minute and higher.
In the air handling art wherein systems have been developed for providing fresh air and return air to structures using suitable fans, it is known that turning vanes to redirect the direction of the airflow into or out of a fan unit can provide excellent turning performance including uniform airflow with minimum pressure loss. The use of such turning vanes in combination with sound attenuating material has proven to be effective in air supplying and air conditioning applications involving the use of axial fan units. Most of these systems employ conventional acoustic dissipative media such as fibreglass. In many of these recently developed systems the sound absorbing surface comprises a special sandwich construction consisting of a perforated cover sheet, an erosion resistant duct-liner and bulk fibre located behind the duct liner and packed to the proper density. However as far as applicant is aware, this sound attenuating technology has in general not been used with nor proposed for use with gas turbines such as large, stationary gas turbines used for the production of power.
It is an object of the present invention to provide a novel sound attenuating duct unit suitable for connection to the outlet of a stationary gas turbine or other noise-creating, gas flow-producing device, this unit being capable of manufacture at a reasonable cost while having substantial sound attenuating capabilities.
According to one aspect of the invention, a sound attenuating duct unit suitable for connecting to an outlet of a stationary gas turbine includes a housing having a horizontal housing section and a vertical housing section and having sidewalls surrounding a main airflow passageway that extends along a substantial bend. An air inlet is located at one end of the horizontal housing section and is adapted for connection to the outlet of the gas turbine. At least one air outlet is located at least proximate to an upper end of the vertical housing section. At least two splitters are mounted in the housing. The splitters divide sections of the main airflow passageway into smaller air passageways. At least one of the at least two splitters is positioned downstream in the main airflow passageway relative to at least another of the at least two splitters. The at least two splitters contain sound attenuating material selected from a group of materials comprising ceramic fibers and mineral wool and capable of withstanding airflow temperatures in the main airflow passageway of at least 500 degrees Celsius. The at least two splitters each contain a fine metal screen having 200 or more strands per inch and covering the sound attenuating material. The metal screen is provided to prevent the sound attenuating material from escaping the splitters. At least a substantial portion of both the sidewalls surrounding the main airflow passageway and metal sidewalls forming the splitters are made of perforated sheet metal having a thickness of at least 12 gauge.
In one embodiment of this outlet silencer for a turbine, the perforated sheet metal is made of stainless steel.
According to another aspect of the invention, there is provided a combination of a gas turbine intended for installation and use at a selected stationary site and a sound attenuating duct unit connected to a hot air exhaust outlet of the gas turbine. The duct unit includes a housing having a horizontal housing section and a vertical housing section and having sidewalls surrounding a main airflow passageway that extends along a substantial bend. There is an air inlet located at one end of the horizontal housing section and connected to the exhaust outlet of the gas turbine. At least one air outlet is located at least proximate to an upper end of the vertical housing section. The combination also includes at least two splitters mounted in the housing. The splitters divide sections of the main airflow passageway into smaller air passageways. At least one of the at least two splitters is positioned downstream in the main airflow passageway relative to at least another of the at least two splitters. The splitters contain sound attenuating material selected from a group of materials comprising mineral wool and ceramic fibers and capable of withstanding airflow temperatures in the main airflow passageway of at least 500 degrees Celsius. A layer of fine stainless steel screen having 200 or more strands per inch is arranged over the sound attenuating material so as to prevent escape of sound attenuating material into the main airflow passageway. Also at least a substantial portion of both the sidewalls surrounding the main airflow passageway and metal sidewalls forming the splitters are made of perforated sheet metal. The screen is arranged behind the perforated sheet metal of the splitters.
In a preferred embodiment of this combination each splitter includes a rounded nose portion, and this nose portion is made of imperforate stainless steel.
According to a further aspect of the invention, a sound attenuating duct unit suitable for connection to an outlet of a stationary gas turbine includes a housing having metal exterior walls, perforated interior walls forming a main airflow passageway and mounted and supported by the exterior walls, a hot gas inlet at one end of the housing and adapted for connection to the outlet of the gas turbine, and at least one gas outlet. The main airflow passageway extends between the gas inlet and the at least one outlet. Sound attenuating members are mounted within the main airflow passageway and are supported therein by the housing. Sound attenuating material is arranged in the housing between the interior walls and the exterior walls and is capable of withstanding high airflow temperatures generated at the outlet of the gas turbine during use thereof. Metal mounting plates having outer edges connected to the exterior walls and inner edges connected to the interior walls are also provided. Spaced apart connecting pins are attached to these mounting plates, project from at least one of the inner edges and the outer edges and extend through oversized holes that are larger than the widths of the respective pins. The holes are formed in at least one of the interior walls and the exterior walls. An attachment device is provided for movably connecting each connecting pin to the at least one of the interior walls and the exterior walls. When the interior walls are heated to an elevated high temperature by operation of the gas turbine, the interior walls are able to expand and move relative to the exterior walls while remaining securely attached to and supported by the exterior walls via the connecting pins and the metal mounting plates.
Preferably, the connecting pins project from the inner edges of the mounting plates and the mounting plates are rigidly attached to the exterior walls of the housing. In this version, the oversized holes are formed in the interior walls.
According to yet another embodiment of the invention, a sound attenuating duct unit suitable for connection to an outlet for hot emission gases produced by a power plant includes a metal housing formed with sidewalls containing sound attenuating material capable of withstanding high airflow temperatures and forming a main airflow passageway for the hot emission gases. The housing has a gas inlet at one end of the housing and at least one air outlet at an opposite end of the housing. The airflow passageway extends between the gas inlet and the at least one gas outlet. The side walls of the housing include exterior wall panels and perforated interior wall panels spaced apart from the exterior panels. The sound attenuating material is sandwiched between the exterior wall panels and the interior panels. At least one elongate sound attenuating splitter is mounted in the main airflow passageway and extends between and is supported by two of the side walls located on opposite sides of the housing. This splitter divides the main airflow passageway into smaller airflow passageways. The or each splitter contains sound attenuating material and has an exterior constructed with perforated sheet metal. Splitter mounting devices connect opposite sides of the at least one splitter directly to the the exterior wall panels so as to allow thermal expansion of the at least one splitter when the duct unit is heated up by the hot emission gases during operation of the power plant.
In the preferred embodiment, each splitter mounting device comprises a bracket rigidly attached to a respective adjacent side wall of the housing and having an inwardly projecting tongue. The or each splitter has side edge plates provided with elongate openings receiving the tongues of the respective brackets for the splitter. Each tongue is movable relative to its respective elongate opening upon thermal expansion of the adjacent attached splitter.
According to a further embodiment of the invention, a sound attenuating duct unit suitable for connecting to an outlet of a noise creating, gas-flow producing device includes a housing having a horizontal housing section and a vertical housing section and having sound attenuating side walls surrounding a main airflow passageway that extends along a substantial bend. A gas inlet is located at one end of the horizontal housing section and is adapted for connection to the outlet of the gas flow producing device. At least one gas outlet is located at least proximate to an upper end of the vertical housing section. At least one initial, sound attenuating splitter is mounted in the housing and has an upstream end in the region of the gas inlet. This at least one splitter extends lengthwise around the substantial bend. A plurality of spaced-apart, sound attenuating, downstream splitters divide the main air flow passageway into smaller airflow passageways and are arranged side-by-side one another. The downstream splitters are located downstream in the direction of gas flow from the at least one initial splitter and have major lower portions extending in substantially parallel planes that are substantially perpendicular to a central widthwise-extending plane defined by an upper end portion of the at least one initial sound attenuating splitter.
In one preferred embodiment, there is only one initial sound attenuating splitter which is arranged substantially centrally in the main airflow passageway and there are three of the downstream splitters. Each of these splitters contain sound attenuating material capable of withstanding gas flow temperatures of at least 500 degrees Celsius.
Further features and advantages will become apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings.